In a known boat steering device of this type, the piston cylinder device, the servo valve and the tubular element which is limitedly displaceable form an integrated servo unit. The tubular element serving as an operating element for the servo valve forms in this case the rigid tube to which the operating cable casing is connected and which forms a guide for the operating rod.
Such a servo-assisted steering arrangement requires greater space athwartships (transversely to the boat) than a non-servo-assisted cable steering arrangement, due to the fact that the mounting of the cable casing in the guide tube of the operating rod is displaced when the cable with its operating rod is moved from its ordinary guide tube to the tubular element which is integrated with the servo valve of the servo-unit. This can create problems in boats in which the engine insulation is such that the space athwartships between for example a steering arm of a rudder or a steerable outboard drive-unit and the boat hull is limited. The reason that problems arise when the distance between the steering arm and the hull is small is that the radius of curvature of the operating cable will be small. This results, on the one hand, in increased friction between the cable and the casing and on the other hand to tensions which affects the control of the servo valve. Especially in boats with double engines with outboard drive units, in which the cable steering arrangement is connected to the steering arm of one of the drive units and is connected to the steering arm to the other drive unit via a tie rod, the space available can make it impossible to use a servo-unit of the type described.